Management practices that may increase soil organic matter (SOM) storage include
conservation tillage, especially no till (NT), enhanced cropping intensity, and
fertilization. My objectives were to evaluate management effects on labile [soil microbial
biomass (SMB) and mineralizable, particulate organic matter (POM), and hydrolyzable
SOM] and slow (mineral-associated and resistant organic) C and N pools and turnover in
continuous sorghum [Sorghum bicolor (L.) Moench.], wheat (Triticum aestivum L.), and
soybean [Glycine max (L.) Merr.], sorghum-wheat/soybean, and wheat/soybean
sequences under convent ional tillage (CT) and NT with and without N fertilization. A
Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochepts) in southern central
Texas was sampled at three depth increments to a 30-cm depth after wheat, sorghum, and
soybean harvesting. Soil organic C and total N showed similar responses to tillage,
cropping sequence, and N fertilization following wheat, sorghum, and soybean. Most
effects were observed in surface soils. NT significantly increased SOC. Nitrogen
fertilization significantly increased SOC only under NT. Compared to NT or N addition,
enhanced cropping intensity only slightly increased SOC. Estimates of C sequestration
rates under NT indicated that SOC would reach a new equilibrium after 20 yr or less of
imposition of this treatment. Labile pools were all significantly greater with NT than CT
at 0 to 5 cm and decreased with depth. SMB, mineralizable C and N, POM, and
hydrolyzable C were highly correlated with each other and SOC, but their slopes were
significantly different, being lowest in mineralizable C and highest in hydrolyzable C.
These results indicated that different methods determined various fractions of total SOC.
Results from soil physical fractionation and 13C concentrations further supported these
observations. Carbon turnover rates increased in the sequence: ROC < silt- and clayassociated
C < microaggregate-C < POM-C. Long-term incubation showed that 4 to 5%
of SOC was in active pools with mean residence time (MRT) of about 50 days, 50% of
SOC was in slow pools with an average MRT of 12 years, and the remainder was in
resistant pools with an assumed MRT of over 500 years.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3831 |
| Date | 16 August 2006 |
| Creators | Dou, Fugen |
| Contributors | Hons, Frank M. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 626085 bytes, electronic, application/pdf, born digital |
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